1. Technical Field
The present invention relates to a separation technique which is aimed at recycling used home appliances and separates resin pieces of a specific constituent substance and resin pieces of another constituent substance from a separation subject in which resin pieces of multiple types are mixed.
2. Description of the Related Art
In recent years, economic activity represented by mass production, mass consumption, and mass disposal have been aggravating environmental problems on a global scale, such as global warming and depletion of resources. Under such circumstance, also in our country, Home Appliance Recycling Law came into effect and obliges recycling of used air conditioners, televisions, refrigerators/freezers, and washing machines, with the aim of building a recycling society.
Conventionally, unneeded home appliances have been recycled by crushing and then separating them by material, using magnetism, wind, oscillation, etc., in home appliance-recycling plants. In particular, the recycling rate of metal materials is high because the use of a specific-gravity separation device or a magnetism separation device allows these materials to be separated by material such as iron, copper, aluminum, etc., and thus recovered in very pure form.
As to resin materials, polypropylene (hereinafter denoted as PP), which has a low specific gravity, is separated from a component having a high specific gravity through specific gravity segregation using water and thus recovered with a relatively high degree of purity. This specific gravity segregation using water, however, has significant problems in that an enormous amount of wastewater is produced and that polystyrene (hereinafter denoted as PS) and acrylonitrile-butadiene-styrene (hereinafter denoted as ABS), which have similar specific gravities, are not separated from each other. In addition, PP contains a filler, which is high in specific gravity and has seen increased demand in recent years, cannot be dealt with by the traditional specific gravity segregation.
A separation method in view of the above problems related to recycling of resin materials has been proposed in Japanese Unexamined Patent Application Publication No. 2002-263587.
The technique disclosed in JP 2002-263587 uses a substance distinguishing unit to detect a constituent substance, thereby enabling separation of resin materials which are inseparable by specific gravity.
To be specific, resin-mixed items conveyed on a conveyor belt are distinguished with the substance distinguishing unit, and in order to separate the distinguished items made of specific resin substance in a drop path of the resin-mixed items shot out of a conveying end of the conveyor belt, pulse air is shot out of a pulse air nozzle so that the items of specific resin substance are blown across a free-fall position of the resin-mixed items and thus separated from them.
This separation method enables separation of PS and ABS, which have similar specific gravity, and is applicable also to separation of PP containing filler, which has high specific gravity.